Sandy Hook madman Adam Lanza wore earplugs as he blew away 20 schoolkids and six adults last month — and investigators say it may have been because the cowardly killer didn’t want to hear his tiny victims’ screams.

“It’s just weird [that he popped them in] given what he was about to go do,’’ one source told the Hartford Courant.

“It’s not like he had to worry about long-term protection of his hearing, because he had to know he wasn’t coming back out of the building.’’

Lanza would have been used to wearing the earplugs during his trips with his mother, Nancy, to shooting ranges, sources said.

The plugs were still in Lanza’s ears when his body was found in slain teacher Victoria Soto’s first-grade classroom.

Before he killed himself as the cops closed in, Lanza had been wildly changing his gun magazines — even discarding some that were still half full — as he moved through the Newtown, Conn., elementary school, mowing down terrified kids and educators, the sources said.

He used only 15 bullets in one 30-round clip before tossing it to the floor and pulling out another magazine that was fully loaded, sources said.

The obsessive changing of clips may have stemmed from Lanza’s playing of violent video games, sources said.

Experienced gamers typically won’t enter a “room’’ or “building” without having fully loaded weapons so that they’re never caught without enough ammo.

Sources told the paper that the macabre Lanza wore all black that day, except for an olive-green utility vest — which had its pockets stuffed with 30-round clips for his Bushmaster AR-15 assault rifle.

He got off about 150 rounds before committing suicide with one of the two pistols he was carrying.

Probers said it took them more than a week to retrieve all the bullets, which were found stuck under doors and in walls and carpets.

The students who survived the massacre returned to class at a different school last week.

The mayor of the nearby town of Stratford, where Soto grew up, yesterday said he wants to name a new elementary school after the 27-year-old teacher, who died shielding some of her young charges.

“She gave her life protecting children, and we must make sure her sacrifice is never forgotten,” Mayor John Harkins said in a statement.

On Dec. 17, a 17-year-old white-supremacist student in Seale allegedly started planning to attack at least six students and one educator using homemade bombs — and the date, three days after Sandy Hook, was no coincidence, officials said.